The invention generally relates to methods for modifying the surfaces of substrates and, more particularly to methods for forming molecular gradients on substrates.
The deposition of self-assembled monolayers (SAMs) made of either mercapto-terminated molecules attached to gold (or other noble metals) or chlorosilane- (or alkoxysilane-) terminated moieties anchored to hydroxyl-terminated substrates offers one of the highest quality routes for systematically and reproducibly tuning the surface properties of materials. By controlling the chemical composition of the terminal group, the length, and microstructure of the SAM molecule, the chemical and physical properties, including wetting, adhesion, friction, and biosensing, can be successfully tailored. While early studies concentrated mainly on preparing substrates with laterally homogeneous SAMs, recent advances in the field allow for creating SAMs with two-dimensional chemical patterns. See Xia, Chem. Rev. 99, 1823-1848 (1999). In particular, the microcontact printing (xcexcCP) technique has proven to be a convenient method for preparing chemically patterned substrates.
While xcexcCP is useful for decorating materials substrates with a variety of motif shapes and dimensions, it typically produces sharp boundaries between the distinct chemical substrate regions. However, for some applications, it is desirable or required that the wetting properties of the substrate change gradually over a certain region in space. This situation can be accomplished by producing surfaces with a gradually varying chemistry along their length. In these so-called gradient surfaces, the gradient in surface energy is responsible for a position-bound variation in physical properties, most notably the wettability. For example, gradient surfaces can be particularly useful in studying interactions in biological systems, as the influence of the entire wettability spectrum upon protein adsorption or cellular interactions can be obtained in one single experiment. While methods to prepare such gradient substrates have been described previously, none of the currently used techniques are believed to provide a complete control over all gradient parameters, including, in one example, the wettability of the two opposite gradient sides and the steepness of the gradient region in between.
Conventional techniques are known for preparing surfaces whose surface energies vary gradually over a certain distance. These techniques are typically rather cumbersome and involve various xe2x80x9cwet chemistryxe2x80x9d surface treatments, which is often times hard to control and not applicable to all materials. For practical application, it is thus desirable to develop methods that would both eliminate the xe2x80x9cwet chemistryxe2x80x9d environment and produce surfaces with reproducible and tunable surface properties. Chaudhury and Whitesides showed that these limitations could be overcome by creating chemical gradients by vapor deposition. See Chaudhury and Whitesides, Science, 256, 1539-1541 (1992). In their experiment, a container with chlorosilane-based molecules (Rxe2x80x94SiCl3) mixed with paraffin oil is placed on one side of a silicon wafer. By varying the relative amounts of Rxe2x80x94SiCl3 and the paraffin oil, the concentration of Rxe2x80x94SiCl3 can be conveniently adjusted. Sufficiently short molecules (up to ca. Rxe2x95x90xe2x80x94(CH2)14H) have high enough vapor pressure so that they evaporate even at a room temperature. As the chlorosilane evaporates, it diffuses in the vapor phase and generates a concentration gradient along the substrate. Upon impinging on the substrate, the Rxe2x80x94SiCl3 molecules react with the substrate xe2x80x94OH functionalities and form an organized SAM. According to this reference, the kinetics of the whole process is controlled predominantly by the vapor diffusion of Rxe2x80x94SiCl3, so that the vapor gradient gets imprinted onto the silica substrate.
According to method embodiments of the present invention, a method for forming a chemically patterned surface includes subjecting a surface of a substrate to a fluid including a component such that the component reacts with the surface to form a first distribution of the component on the surface. Thereafter, the surface is deformed along at least one axis such that the first distribution of the component is converted to a second distribution different from the first distribution. The second distribution is a gradient of the component.
According to further method embodiments of the present invention, a method for forming a patterned surface includes enlarging a substrate having an initial surface portion to form an enlarged surface portion from the initial surface portion. A functional group is then conjugated on the enlarged surface portion. The substrate is then reduced to form a reduced surface portion from the enlarged surface portion, with the reduced surface portion having an area less than the enlarged surface portion, and with the reduced surface portion having the functional group deposited therein at a greater density than the enlarged surface portion. The functional group in the enlarged surface portion forms a density gradient.
According to further method embodiments of the present invention, a method for forming a chemically patterned surface includes subjecting a surface of a substrate to a vapor including a first component such that the first component reacts with the surface to form a first distribution of the first component on the surface. The first distribution is a gradient of the first component. The surface of the substrate is subjected to a fluid including a second component such that the second component reacts with the surface to form a second distribution of the second component on the surface. The second distribution is a gradient of the second component. The gradients of the first and second distributions extend in different directions.
According to further method embodiments of the present invention, a method for forming a chemically patterned surface includes providing a mask on a surface of a substrate to form at least one exposed portion of the surface not covered by the mask and at least one covered portion of the surface covered by the mask. The surface is subjected to a fluid including a component such that the component reacts with the at least one exposed portion and is prevented from reacting with the at least one covered portion by the mask. The component reacted with the at least one exposed portion forms a distribution of the component on the surface, the distribution being a gradient.
Objects of the present invention will be appreciated by those of ordinary skill in the art from a reading of the figures and the detailed description of the preferred embodiments which follow, such description being merely illustrative of the present invention.